By all measures, the Clippers should be buried after a first quarter in which they give up 31 points on 24 possessions. Guards are getting to the rack at will on the Clippers, whether it’s Rajon Rondo, Will Bynum, or even Roko Ukic. Rondo shreds the Clippers defense tonight in the first period for 13 points on 5-5 FGs — three of these FGMs occur at the basket, and another couple at short range. Why are opposing guards beating the Clips? Most of the time, you can chalk it up quite generally to “Bad S/R Defense,” but there’s a multitude of more specific reasons:

Baron Davis is a step slow [1st, 4:54]: There isn’t a lot to undress here, only that guards of Rondo’s youth, speed, and agility are having their way against Davis. Here, Baron does a good job of getting back in transition off the long Zach Randolph miss from 20 feet. Eric is waiting for Rondo at the foul line, which is probably where you want to pick up the Celtics’ speedster. Baron’s feet are set and he’s aware of what’s coming, but none of this is a deterrence to Rondo, who drives directly at Baron’s left hip. Rondo breezes past Baron and in one fluid motion, he gathers the ball with those long arms, squares, and touches his shot off the top of the glass for a layup.

Bad decisions in transition [1st, 10:40] Eric Gordon’s strength makes a him an effective defender against many 2s, even most of those to whom he gives up an inch or two, but like most rookies, Eric gets crossed up when his team isn’t set defensively. Here, we see again that long misses on the offensive end wreck havoc on your defense, particularly when a guy like Rondo is at point. Baron heaves up a contested fall-away 20-footer that Rondo collects in stride, and ignites the transition for Boston. Marcus Camby picks up Rondo at the foul line, which forces the Celtics’ PG to kick the ball back to Ray Allen at the perimeter. Rondo then floats to the left baseline, where there isn’t a Clipper in close proximity. Baron is slow, but he’s generally smart defensively, and from the moment the Celtics get out in the open floor, he attaches himself to Ray Allen.

When we freeze on the screen, Allen and Pierce are accounted for by Davis and Mardy Collins respectively; Camby mans the paint in Camby-mode — with one eye on the ball, the other on Kendrick Perkins; Zach stands on the weak side between Kevin Garnett and the ball; but Eric Gordon is confused. He sees that his man, Allen, is covered by Baron, but doesn’t process that Rondo is standing to his right all alone on the baseline. Zach shoves him in that direction, but by the time Eric figures it out, Rondo finishes the uncontested drive with an easy layup.

This isn’t to pick on Eric — he’s had a stellar defensive campaign in his rookie season. But he needs to recognize that as the speedy guard in the Clips’ backcourt, he’s going to have assignments — particularly in transition — that aren’t in the textbook, much the way Rondo picks up the ball on the break, even when it’s Allen’s man.

Unresponsive help defense [1st, 1:05]: Gordon is now on Rondo, as Fred Jones has replaced Baron in the lineup. Perkins — who has never set a legal pick in his 24 years — gives Rondo a high screen to go left. Kaman picks him up on the switch, and does a decent job of staying between Rondo and the basket.

Here’s a little nuance that shows you why the Celtics are so good and the Clippers are so lousy. Once Rondo takes the left dribble lane, Eddie House clears out and dashes to the perimeter. On first blush, it doesn’t look like anything more than incidental motion on the court, but House’s cut denies Fred Jones the opportunity to help on Rondo. So who’s the help for the Clippers? Zach Randolph, whose man, Glen Davis, is now out of the play. Zach doesn’t follow Davis to the perimeter [nor should he with the ball in Rondo’s hands on the other side of the floor], but he never reacts to Rondo either. He doesn’t move.

At the risk of beating this to death, just think about the following: Go through the catalog of starting NBA PFs, and imagine how each reacts to this help scenario: Glen Davis [the PF’s man] out of the play, with Rajon Rondo en route to the basket. Even Amare Stoudemire feigns interest once in a while, doesn’t he?

The Clippers get a reprieve in the second quarter, when a ragtag collection of Boston reserves makes only two shots over a nine-minute span, allowing the Clippers to erase a 13-point deficit, and build a 3-point lead. Chris Kaman is starting to find his rhythm [he’s 20 for his last 30 from the field], and his face-up 15-footer appears more decisive than at any point since Thanksgiving. Steve Novak finds plenty of real estate along the arc in transition and splashes a couple of 3PMs that keep the run going. Kaman and Randolph look comfortable on the floor together throughout the second quarter. They control the glass with a 14-6 margin and don’t allow Boston a single offensive rebound. Kaman assumes the high post, which seems to be the best place for him right now, while Randolph does his thing on the low block.

The Celtics surge past the Clips in the third quarter, when Boston drills seven consecutive shots — five of the seven at the basket. Ray Allen toys with Eric Gordon. He lures the rookie to the outside, then beats him with a baseline cut for an easy layup [3rd, 8:38]. A couple minutes later he snookers Eric with an up-fake, working himself plenty of space to drain an 18-footer [3rd, 5:45]. Finally, he drives directly at Gordon in transition, finishing with a beautiful runner [3rd, 4:11]. After a timeout, Allen makes it an 11-0 run when Baron traps Pierce with the ball up top. This allows Rondo to move into Eric’s space, forcing the rookie to choose between picking up the roving Rondo inside, or chasing Allen out to the arc, where the sharpshooter built a hall-of-fame career.

Good teams force their opponents to choose between two undesirable outcomes, and that’s what the Celtics do repeatedly to the Clippers in the third quarter. Eric does the right thing here, but it doesn’t matter. Boston already got what it wanted — Camby on Pierce out on the perimeter. Baron doesn’t feel he can leave; Allen recognizes it instantly, and Eric can’t be in two places at once. Bingo.